This invention relates to the prevention of unwanted immune responses to foreign antigens.
Foreign antigens (e.g., recombinant proteins) administered to mammals, e.g., humans, for therapeutic purposes can cause unwanted immune responses, i.e., the formation of antibodies against the foreign antigen. Such immune responses can occur even where the antigen is the recombinant form of a naturally-occurring human protein, e. g., tissue plasminogen activator, because such a protein, even if having the same amino acid sequence as the natural protein, can be glycosylated in such a way as to cause the protein to appear foreign to the immune system. Thus, the term "foreign antigen" as used herein refers to any substance which is not identical to a substance naturally present in the mammal being treated. A goal of medicine is to be able to administer foreign therapeutic agents such as recombinant proteins, without evoking an unwanted immune response, i.e., to induce tolerance to the therapeutic agent. (Tolerance as used herein means the suppression of the ability to mount a humoral immune response to a foreign antigen upon re-challenge with that antigen, even after the substance inducing the suppression has been cleared from the bloodstream.)